You can earnRP by challenging someone to a duel in our battle arena's.

The first one being the battle Arena. You can challenge an opponent to a match. For each match won you obtain 50RP. You can also challenge your opponent to a shadow duel. With these matches you can specify the amount being wagered. However the winner takes the RP as usual, but that same amount of RP is also lost from your opponents total amount of RP.